1. Field of the Invention
The present invention is related to the field of prosthetic mechanical replacement valves for human implantation. More particularly, the present invention is directed to a mechanical heart valve which includes a base portion which is attachable to a patient's heart tissue in place of a natural heart valve. The valve includes a base portion which defines a through blood passageway. The blood passage way is occluded by a movable valve member assembly having at least a pair of valve leaflets movable between a first position and a second position. In the first position the valve leaflets cooperate with one another and with the base portion to close the blood passageway. The leaflets are pivotal to a second fully open position in which the leaflets swing away from sealing cooperation with one another into a position close to axial alignment with the passageway to open blood flow therethrough. The leaflets are interrelated with one another to yieldably bias the leaflets toward a partially open third pivotal position intermediate of the first and second positions.
2. Related Technology
A mechanical heart valve is known according to U.S. Pat. No. 4,276,658, issued Jul. 7 1981 to St. Jude Medical, Inc., of St. Paul Minn. and disclosing what is generally known as the "St. Jude valve". This mechanical heart valve includes a base portion defining a through blood passageway and pivotally carrying a pair of valve leaflets. The valve leaflets are sealingly cooperable with each other and with the base member to occlude the blood passageway. Alternatively, in response to dynamic blood fluid forces, the leaflets are pivotal to another position opening blood flow in one direction through the blood passageway. The dynamic blood fluid forces are able to pivot the leaflets between their open and closed positions to allow peristaltic pumping of blood by the patient's heart in which the valve is installed.
One recognized disadvantage of the St. Jude valve is that the leaflets do not open in anticipation of a pumping stroke of the heart, as do natural valves. That is, the natural valve will open slightly in response to a balance of fluid blood pressure on each side of the valve. This pressure-balanced anticipatory opening of the natural valves allows a better, more complete filling of the ventricle of the heart. The St. Jude valve which lacks this anticipatory pressure-balanced opening produces a relatively decreased blood pumping efficiency of the heart.
Another recognized disadvantage of the St. Jude heart valve is that the leaflets also do not begin to close in anticipation of the end of a pumping stroke of the heart. As a result, regurgitation blood flow must take place in order to begin and complete closing of the valve. Because the valve leaflets are fully open when this regurgitation flow takes place, the leaflets slam shut from a fully open position. The leaflets thus dynamically impact with one another and with the base member upon movement from their open position to their closed position in sealing cooperation with one another and the base member. A consequence of this impact upon valve closing is an undesirably high wear rate of the valve, and an undesirable impact noise. Generally, this undesirable impact noise can be heard externally of the patient as a clicking noise. While some patients perceive this clicking noise as comforting and indicating that their new prosthetic heart valve is working properly, other patients and some of those around them, view this operating click as undesirable and distracting.
It should be noted that conventional mechanical heart valves of the St. Jude type may demonstrate some asymmetrical and/or asynchronous movement of their valve leaflets in respect to one another. That is, the valve leaflets of a conventional mechanical heart valve may not always move in pivotal symmetry or in pivotal synchronization with one another. Also, the asymmetry or asynchronous motion contributes to an increased closing impact for the trailing one of the valve leaflets.
One solution to this wear, noise, and lack of anticipatory opening of the St. Jude-type valve is presented by U.S. Pat. No. 4,605,408, issued Aug. 12 1986 to Alain Carpentier. According to the teaching of the '408 patent, the leaflets of a mechanical heart valve are biased toward an open position by either a leaf spring device effective while the leaflets are close to their seats, or by a pair of magnets repelling one another. One of the magnets of each pair of magnets is taught to be carried in a leaflet, while the other magnet of each pair is carried by the base member adjacent to the valve seat. The magnets are oriented to repel one another. As a consequence, the valve leaflets are urged away from their seats. The effective bias provides a closing cushion as the leaflets approach their seats, and also urges the leaflets off their seat to provide an anticipatory opening of the valve.
Unfortunately, the teaching of the '408 patent has never been possible to implement in a safe and effective mechanical heart valve. The embodiment having a leaf spring has not been accepted because of the possibility of breakage of the spring and of the broken spring becoming a foreign body movable in the circulatory system. The embodiment having opposed magnets carried by the leaflets and the base member has never been commercially implemented because of a variety of problems with this design. One problem is that the available physical space for locating the magnets in the edge portions of the leaflets (where they must be located to oppose magnets in the base portion) has been too constrained to receive effectively sized magnets. Another problem has to do with locating the magnets in an area of high contact stress, which accelerates fatigue problems with the structure of the valve.
Another proposed solution to the deficiencies of conventional prosthetic mechanical heart valves is presented by U.S. Pat. No. 5,123,918, issued Jun. 23, 1992 to Philippe Perrier, et al. According to the teaching of the '918 patent, a tri-leaflet prosthetic heart valve includes magnets in the leaflet corners which attract one another. This attraction of the leaflets for one another is contrary to anticipatory opening of the leaflets because the magnets attract one another and tend to latch the valve in a closed position. In the open position of the valve the magnets of the leaflets are confronted by like-poled magnets carried in aligned locations of the base portion of the valve. Consequently, these magnets repel one another to urge the leaflets toward a closed position. In other words, the valve leaflets are urged radially inwardly away from the base portion to provide anticipatory closing of the leaflets.
However, this anticipatory closing of the '918 patent is only the result of a bias from the fully open position of the valve toward a closed position. Due to the magnetic attraction of the valve leaflets for one another this valve is also magnetically urged to its closed position. In this design, there does not appear to be any bias of the valve leaflet from their closed position toward a dynamically-stable partially open position intermediate of the closed and fully open positions.
Still another mechanical prosthetic heart valve is known according to European Patent Office publication No.0023797A1. This publication is believed to disclose a mechanical prosthetic heart valve in which the valve leaflets both pivot and translate simultaneously at they move between their open and closed positions. This valve is not believed to provide either anticipatory opening or anticipatory closing of the valve leaflets. There does not appear to be any resilient bias of the valve leaflets toward a particular valve position.
In view of the above, it would be desirable to provide a mechanical heart valve which avoided one or more of the deficiencies of the conventional technology.
Particularly, it would be desirable to provide a mechanical heart valve which cushions the closing motion of the leaflets upon contact with each other and with the base member of the valve.
Additionally desirable features of such a mechanical heart valve would be realized if the valve were to have an anticipatory pressure-balanced opening function and a bias toward synchronous operation of the valve leaflets.
Still another feature of such a mechanical heart valve would be realized if the cushioning effect upon closing of the valve were effective to reduce the noise of operation of the valve.
An additional desirable feature would be to have the leaflets urged resiliently toward a position of anticipatory closing so that the leaflets are not slammed closed from their fully open positions by regurgitation flow.
Further to the above, a desirable feature for such a prosthetic heart valve would be for the valve leaflets to be biased both from their closed position and from their fully open position toward an intermediate partially open and dynamically stable position. This feature provides both anticipatory opening and anticipatory closing of the valve.
Another desirable feature would be for a prosthetic heart valve to have leaflets which have symmetrical or at least synchronous pivotal motions between their open and closed positions.